prefetchw() requires it to be defined by linux/prefetch.h, or it resultsin a compile error:

In file included from drivers/parisc/sba_iommu.c:916:0:drivers/parisc/iommu-helpers.h: In function 'iommu_fill_pdir':drivers/parisc/iommu-helpers.h:62:4: error: implicit declaration of function 'prefetchw'